Moving dynamic test loads for road bridges - a case study
Bayer, Jan; Urushadze, Shota
2019 - English
Two types of dynamic testing load for bridges - driving sprung mass and driving impulse load - areexamined from the drive-by identification point of view. Numerical studies in ANSYS using contact elements and in MATLAB using a modal solution together with coupling force were performed. Equations for the estimation of the impulse load caused by a rolling cogwheel were suggested. The experiments confirmed that a driving impulse load is more efficient in exciting bridge vibrations. This, together with the fact that impulse loading is not sensitive to surface roughness, leads to the conclusion that, as a method for bridge health monitoring, impulse loading is more promising than using a driving sprung mass
Keywords:
drive-by identification; bridge testing; moving sprung mass; impulse loading; vibration measurements; laboratory experimentsAvailable at various institutes of the ASCRMoving dynamic test loads for road bridges - a case study

Two types of dynamic testing load for bridges - driving sprung mass and driving impulse load - areexamined from the drive-by identification point of view. Numerical studies in ANSYS using contact ...

Probability density determination by means of Gibbs entropy probability density
Náprstek, Jiří; Fischer, Cyril
2019 - English
A method of random response investigation of a nonlinear dynam-ical system is discussed. In particular, the solution of the probability density of a single/multi-degree of freedom (SDOF/MDOF) system response is investigated. Multiple stable equilibrium states with possible jumps of the snap-through type among them are considered. The system is Hamiltonian with weak damping excited by a set of non-stationary Gaussian white noises. The solution, which is based on the Gibbs principle of the maximum entropy of probability, can be employed in various branches of engineering. The search for the extreme of the Gibbs entropy functional is formulated as a constrained optimization problem. The secondary constraints follow from the Fokker-Planck equation (FPE) for the system considered or from the system of ordinary di_erential equations for the stochastic moments of the response derived from the relevant FPE
Keywords:
Fokker-Planck equation; Gibbs entropy functional; maximum entropy; probability density principleAvailable at various institutes of the ASCRProbability density determination by means of Gibbs entropy probability density

A method of random response investigation of a nonlinear dynam-ical system is discussed. In particular, the solution of the probability density of a single/multi-degree of freedom (SDOF/MDOF) system ...

Deformation response of polydimethylsiloxane substrates subjected to uniaxial quasi-static loading
Martino, F.; Vinařský, V.; Šleichrt, Jan; Kytýř, Daniel
2019 - English
To investigate cellular response of cardiomyocytes to substrate mechanics, biocompatible material with stiffness in physiological range is needed. Polydimethylsiloxane (PDMS) based material Sylgard 184 is used for construction of microfluidic organ on chip devices for cell culture due to ease of device preparation, bonding, and possibility of surface functionalization. However it has stiffness orders of magnitude out of physiological range. Therefore we adapted recently published protocol [1] aiming to prepare substrates which offer stiffness in physiological range 5−100 kPa using various mixtures of Sylgard 527 and Sylagard 184. The inhouse developed loading device with the loading capacity of 3 kN with 1 μm position tracking accuracy and sub-micron position sensitivity was employed for this experimental campaign. The experiments were controlled by the proprietary LinuxCNC software running on the real-time kernel [2]. All batches of the samples were subjected to monotonic compression loading. During the displacement driven experiment with loading rate 10 μm · s−1 the samples with diameter 12.00 ± 0.05mm and height 14 − 16mm were compressed to minimally 50% deformation. Because of high differences in the samples stiffness various load cells with nominal capacity 50N, 10N, and 1N was used for the most reliable force logging. Material properties for all batches were derived from a set of tests under dry and simulated physiological conditions. The results are represented in the form of stress-strain curves calculated from the acquired force and displacement data and elastic moduli are estimated as secant up to 10% deformation.
Keywords:
compression loading; hyperelasticity; polydimethylsiloxane substratesAvailable at various institutes of the ASCRDeformation response of polydimethylsiloxane substrates subjected to uniaxial quasi-static loading

Wind tunnel tests for lifetime estimation of bridge and mast cables exposed to vortex induced vibrations
Trush, Arsenii; Pospíšil, Stanislav; Kuznetsov, Sergeii
2019 - English
A significant number of TV and radio broadcasting masts in the Czech Republic was built in the 70-80s of the last century. At the moment is an actual issue is the reconstruction and determination of residual life of these structures. Guyed masts and particularly guy ropes have significant dimensions and comparatively low mass and damping with high flexibility. Therefore, aerodynamic and aeroelastic loads, such as vortex induced vibrations, galloping, wind gusts, etc., are key for them. As a tensile construction elements (guy ropes) for guyed masts the traditional open wire spiral strand cables are used. This type of cable has a characteristic helical surface roughness pattern that can act as vortex suppressor, high fatigue endurance, although somewhat lower corrosion resistance comparing to modern locked coil cables with non-circular shaped wires of outer layer and cables with protective polymer coatings. At the same time, on numerous bridges with the above-mentioned modern cable types the fatigue damage to wires in anchorage zones and destruction of protective coatings was detected. Present paper provides results of wind tunnel testing of three models of helical strake cable in order to evaluate separately impact of lay angle and surface roughness factors and reference smooth cylinder model in flow with grid generated turbulence of different intensities. The reduction of the lock-in range of helical strand cables comparing to reference smooth model was observed whereby the greatest impact was an increase of lay angle.
Keywords:
bridge cable; wind tunnel; vortex sheddingAvailable at various institutes of the ASCRWind tunnel tests for lifetime estimation of bridge and mast cables exposed to vortex induced vibrations

A significant number of TV and radio broadcasting masts in the Czech Republic was built in the 70-80s of the last century. At the moment is an actual issue is the reconstruction and determination of ...

In-situ compression test of artificial bone foams in controlled environment using X-Ray micro-computed tomography
Glinz, J.; Kytýř, Daniel; Fíla, Tomáš; Šleichrt, Jan; Schrempf, A.; Fürst, D.; Kastner, J.; Senck, S.
2019 - English
X-RayMicro-computed tomography (XCT) has already become a standard method for investigations of bone and bone replacement materials in medical research. For an in-depth characterization of histomorphometric features, digital volume data acquired by XCT can be processed and visualized three dimensionally to determine parameters such as bone volume fraction, cortical thickness and porosity. In this study, we investigated specimens of artificial bone foams, developed by the research group for surgical simulators at the UAS Linz, which are used to mimic the haptic feedback of physiologic and pathologic bone for more realistic surgery training. Similar specimen of artificial bone foam in a dry state have already been characterized precisely in [1]. However, since physiological bone typically is in a wet state, the main purpose of this study was the investigation of the influence of environmental conditions on artificial bone foams of varying composition. Thus, specimens with two kinds of mineral filler material as well as different amounts of foaming agent were prepared and tested in an in-situ loading stage developed by the ITAM CAS. In this stage, specimens can be immersed in liquid and tested under temperature-controlled conditions. Consequently, a total amount of 12 specimens was subjected to compression loading; half of them immersed in water at 36.5◦C and half in dry condition. Results showed that there is no significant influence of liquid immersion to the compression outcome. However, foams with less amount of foaming agent appeared to have smaller pores resulting in higher compression strength. Different types of mineral filler material also showed no significant influence on compression strength. Furthermore, a time-lapse in-situ investigation with XCT scans in-between the load steps was performed for one specimen immersed in water to investigate behavior during load. Despite of the open porous morphology of the foam, water immersed only partially into the foam, leaving pores closer to the center unfilled. Concluding, the usage of the artificial bone foams investigated is despite their physiologically wet condition also valid in a dry state since environmental differences are nonessential for their mechanical properties.
Keywords:
x-ray micro-computed tomography; artificial bone foams; in-situ testingAvailable at various institutes of the ASCRIn-situ compression test of artificial bone foams in controlled environment using X-Ray micro-computed tomography

X-RayMicro-computed tomography (XCT) has already become a standard method for investigations of bone and bone replacement materials in medical research. For an in-depth characterization of ...

Local stabilization of the quasiperiodic response of the generalized van der Pol oscillator
Fischer, Cyril; Náprstek, Jiří
2019 - English
The generalized van der Pol equation is often used for description of various effects originating in the aero-elasticity of large slender engineering structures. This applies mainly to the quasiperiodic beatings that can be encountered especially in lock-in regimes when the vortex frequency becomes close to the structure eigenfrequency with a small detuning. The current paper presents numerical analysis of influence of the subor superharmonic excitation on the character of the response of a generalized van der Pol oscillator. This way it complements two previous papers of the authors dealing with stability analysis of certain types of the stationary periodic or quasiperiodic response of the system under study.
Keywords:
generalized van der Pol equation; quasiperiodic response; sub- and superharmonic synchronization; beating effect; numerical simulationAvailable at various institutes of the ASCRLocal stabilization of the quasiperiodic response of the generalized van der Pol oscillator

The generalized van der Pol equation is often used for description of various effects originating in the aero-elasticity of large slender engineering structures. This applies mainly to the ...

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